He wasn't fast enough simple as that. Senna showed a few good performances, but unfortunately for him on his day he was good enough to match Maldonado, but on Maldonado's day he was good enough to slaughter Senna.

Pastor is a very underrated driver and it wouldn't surprise me if Senna could put in Di Resta esq performances. His name got him to F1 and it sucks he never made it (when he very nearly did with Honda, I mean with a bit of luck he could be a world champion) but thems the breaks.